GCN Circular 22194

D. A. Perley and K. Taggart (LJMU) report:

We downloaded public, pre-explosion survey data covering the field of
GRB 171205A (D'Elia et al., GCN 22177
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) from a number of public archives:
GALEX (Martin et al. 2005, ApJL 619 1), Pan-STARRS 1 (Chambers et al.
2016, arXiv:1612.05560
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), and 2MASS (Skrutskie et al. 2006, 131 1163).
Photometry of the presumed host galaxy (2MASX J11093966-1235116; Izzo et
al., GCN 22178
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) was obtained from the relevant photometric catalogs for
2MASS (Huchra et al. 2012, ApJS 199 26) and GALEX (Bianchi et al. 2011,
MNRAS 411 2770).  For Pan-STARRS 1, we performed elliptical aperture
photometry on the images ourselves (using a semimajor axis of 19.35" and
axis ratio 0.6) using PS1 field stars for calibration.

We fit the combined SED (including 10 filters: GALEX FUV and NUV,
Pan-STARRS g, r, i, z, and y, and 2MASS J, H, and Ks) using the SED
fitting package LePHARE (Arnouts et al. 1999, MNRAS 310 540; Ilbert et
al. 2006, A&A 457 841).  A redshift of z=0.037 was assumed (Izzo et al.,
GCN 22180
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), and Galactic foreground extinction was taken to be
E(B-V)=0.045 (Schlafly et al. 2011; ApJ 737 103).  We obtain a stellar
mass of log10(M/Msun) = 10.1 +/- 0.1 and a star-formation rate of SFR =
3 +/- 1 Msun/yr.

This host mass is much larger than that of any other low-redshift GRB
with a confirmed SN counterpart.  The next-most-massive SN/GRB host is
that of GRB 120422A (SN 2012bz), with log10(M)~9.0.

In contrast, the majority of low-z (z<0.4) long-duration (>2s) GRBs with
no unambiguous observed SNe are in massive hosts similar to this event.
These include GRBs 060505 (Fynbo et al. 2006, Nature 444 1047), 051109B
(Perley et al., GCN 5387
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), 050219A (Rossi et al. 2014, A&A 572), 050826
(Mirabal et al. 2007, ApJ 661, 127), 080517 (Stanway et al. 2015, MNRAS
226 3911), and possibly 150518A (cf GCN 17903
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, Pozanenko et al).  In
many of these cases an SN was not searched for to deep limits, and
others could be attributed to host extinction, an ambiguous duration
possibly consistent with the "short" GRB class, or confusion of a high-z
GRB with a foreground galaxy.

Nevertheless, it remains possible that host mass (and perhaps
metallicity) is closely connected to whether a luminous SN emerges from
a GRB explosion.  The very long duration, bright UV counterpart, and
early spectroscopy of GRB 171205A all suggest that this is a genuine
(albeit low-luminosity) long GRB and is not extinguished or at high-z,
and it is in a high-mass galaxy (although its position is at the outer
edge of the disk).  Whether or not an SN emerges from this GRB
represents an important test of the tentative host dichotomy suggested
by previous events.  We encourage observers to monitor the photometric
evolution carefully over the coming days and obtain deep, multiband
photometry and spectroscopy, especially if a clear rising SN does not
emerge.

[GCN OPS NOTE(15dec17: Per author's request, the first-author Kann
reference was corrected to be Izzo.]